This way guaranties me total control over mapping and allocating slots.

When I am using rankfile mapper, I know exactly what and where I am putting, OS can easily oversubscribe my CPU with unmapped by rankfile processes. I am also not sure how it will effect users that have schedulers.

I am also not sure that users, who got used to work with hostfile would change their scripts according to the mapper.

Had a chance to think about how this might be done, and looked at it for awhile after getting home. I -think- I found a way to do it, but there are a couple of caveats:

1. Len's point about oversubscribing without warning would definitely hold true - this would positively be a "user beware" option

2. there could be no RM-provided allocation, hostfile, or -host options specified. Basically, I would be adding the "read rankfile" option to the end of the current allocation determination procedure

I would still allow more procs than shown in the rankfile (mapping the rest bynode on the nodes specified in the rankfile - can't do byslot because I don't know how many slots are on each node), which means the only change in behavior would be the forced bynode mapping of unspecified procs.

So use of this option will entail some risks and a slight difference in behavior, but would relieve you from the burden of having to provide a hostfile. I'm not personally convinced it is worth the risk and probable user complaints of "it didn't work", but since we don't use this option, I don't have a strong opinion on the matter.

Let's just avoid going back-and-forth over wanting it, or how it should be implemented - let's get it all ironed out, and then implement it once, like we finally did at the end with the whole hostfile thing.

Let me know if you want me to do this - it obviously isn't at the top of my priority list, but still could be done in the next few weeks.

Ralph

On Jun 21, 2009, at 9:00 AM, Lenny Verkhovsky wrote:

Sorry for the delay in response,

I totally agree with Ralph that it's not as easy as it seems,

1. rankfile mapper uses already allocated machines ( by scheduler or hostfile ), by using rankfile as a hostfile we can run into problem where trying to use unallocated nodes, what can hang the run.

2. we can't define in rankfile number of slots on each machine, which means oversubscribing can take place without any warning.

3. I personally dont see any problem using hostfile, even if it has redundant info, hostfile and rankfile belong to different layers in the system and solve different problems. The original hostfile ( if I recall correctly ) could bind rank to the node, but the syntax wasn't very flexible and clear.

1. let's change the error message as this is easily done and thus can be done now

2. I can look at how to eat the rankfile as a hostfile. This may not even be possible - the problem is that the entire system is predicated on certain ordering due to our framework architecture. So we get an allocation, and then do a mapping against that allocation, filtering the allocation through hostfiles, -host, and other options.

By the time we reach the rankfile mapper, we have already determined that we don't have an allocation and have to abort. It is the rankfile mapper itself that looks for the -rankfile option, so the system can have no knowledge that someone has specified that option before that point - and thus, even if I could parse the rankfile, I don't know it was given!

What will take time is to figure out a way to either:

(a) allow us to run the mapper even though we don't have any nodes we know about, and allow the mapper to insert the nodes itself - without causing non-rankfile uses to break (which could be a major feat); or

(b) have the overall system check for the rankfile option and pass it as a hostfile as well, assuming that a hostfile wasn't also given, no RM-based allocation exists, etc. - which breaks our abstraction rules and also opens a possible can of worms.

Either way, I also then have to teach the hostfile parser how to realize it is a rankfile format and convert the info in it into what we expected to receive from a hostfile - another non-trivial problem.

I'm willing to give it a try - just trying to make clear why my response was negative. It isn't as simple as it sounds...which is why Len and I didn't pursue it when this was originally developed.

Being a part of these discussions I can understand your reticence to reopen this discussion. However, I think this is a major usability issue with this feature which actually is fairly important in order to get things to run performant. Which IMO is important.

That being said I think there are one of two things that could be done to mitigate the issue.

1. To eliminate the element of surprise by changing mpirun to eat rankfile without the hostfile. 2. To change the error message to something understandable by the user such that they
know they might be missing the hostfile option.

Again I understand this topic is frustrating and there are some boundaries with the design that make these two option orthogonal to each other but I really believe we need to make the rankfile option something that is easily usable by our users.

--td

Ralph Castain wrote:

Having gone around in circles on hostfile-related issues for over five years now, I honestly have little motivation to re-open the entire discussion again. It doesn't seem to be that daunting a requirement for those who are using it, so I'm inclined to just leave well enough alone.

It seems to me that the rankfile has sufficient information to express what I want it to do. But mpirun won't accept this. To fix this, I have to, e.g., supply/maintain/specify redundant information in a hostfile or host list.

So the files are intentionally quite different. Trying to combine them would be rather ugly.

Right. And my issue is that I'm forced to use both when I only want rankfile functionality.

In order to use "mpirun --rankfile", I also need to specify hosts/hostlist. But that information is redundant with what I provide in the rankfile. So, from a user's point of view,
this strikes me as broken. Yes? Should I file a ticket, or am I missing something here about this functionality?